For a rationalization and automation of production lines, the so-called machining centers (multiple-duty machine tools) each able to perform a variety of machining operations such as milling, tapping, boring, etc. automatically and with high efficiency have been widely employed. Such a machining center generally has a positioning function for setting a workpiece in position automatically and a machining function for performing milling, tapping, boring and/or other machining work on an elected part of the workpiece, and carries as incorporated therein a variety of tools necessary for such operations as securely mounted on respective tool holders. As such, the machining center performs the intended machining as the tool required therefor is automatically selected from the battery of tools, taken out together with the tool holder as a unit, and mounted on the lower end of the spindle of the machining center.
FIG. 21 shows a machining tool and tool holder as so mounted as a unit on the machining center spindle. It is a longitudinal section view showing the spindle and associated assembly of the machining center. In the drawing, the reference numeral 1 designates a spindle for imparting a rotary motion to a tool 13 for the machining of a workpiece and the numeral 2 designates a tool holder mounted at the lower end of said spindle 1. The tool holder 2 is described below in detail. The tool holder 2 comprises a frustoconical mating member 4 complementary to a tapered inner wall 3 of said spindle 1 in proximity with its lower end, a grippable member 6 projecting in the manner of a bolt from the center of the upper surface of said mating portion 4 and engageable with a chuck member 5 disposed within said spindle 1, an arm-engaging member 8 formed on the bottom of said mating member 4 and having a groove 7 adapted to engage with a tool mounting-dismounting arm (not shown) of the machining center, and a tool coupling shaft 9 extending downwards from the center of the lower end of said arm-engaging member 8. The tool 13 is set in position at the lower end of the tool coupling shaft 9 of the tool holder 2 and is secured in position by means of a lock screw 10.
In this arrangement, the machining center performs a machining operation as follows. First, a workpiece is set on a work table (not shown) disposed under said spindle 1. The table is adapted to slide in X- and Y-directions in accordance with a pre-inputted program and positions the workpiece at the machnining start point (origin) for the workpiece. Then, the spindle 1 begins to rotate to cause the tool holder 2 and tool 13 to spin as a unit and, at the same time, said work table ascends (or the spindle 1 descends) to bring the edge or point of the tool 13 into contact with the portion of the workpiece to be machined, whereby the desired machining of the workpiece is initiated. With a constant shift of the table or the spindle 1 in accordance with the pre-inputted program, the position of contact of the workpiece with the tool point is constantly varied, thereby giving a predetermined finished shape to the workpiece. After completion of the above continuous series of operations, the pressure contact between the tool 13 and the workpiece is relieved and the machined work is taken out from the table. When a plurality of workpieces are to be machined in the same way, a new workpiece is fed onto the table as soon as the machined work is taken out and the above series of operations is performed once again so that continuous automatic machining is carried out.
Now, even in such automatic machining with a machining center, just as in the ordinary machine tool operation, there are cases in which a cutting fluid or grinding fluid must be supplied and, therefore, a fluid nozzle means for delivering such a cutting or grinding fluid is incorporated in the machining center.
However, in spite of the fact that the machining direction of the tool 13 with respect to the workpiece is determined as aforementioned by the relative position of the table carrying the workpiece and the spindle 1, the delivery of the cutting or grinding fluid is generally done from a delivery nozzle fixed in a position quite indifferent to the movements of the table and spindle 1 within the machining center. Thus, the fluid is delivered without regard to the machining direction of the tool 13 with respect to the workpiece. Therefore, whereas the effect of cooling ought to be directed mainly to the point where the most intense heat is generated in machining such as cutting, grinding, etc., that is the critical point (machining point) where the edge or point of the tool 13 enters into the workpiece, the fluid is delivered off the mark so that the generated heat of machining cannot be fully controlled with consequent problems such as serious damages to the tool 13.
Therefore, it is common practice to employ an elongated jet nozzle 150 that can be finger-controlled in the direction of delivery as illustrated in FIG. 22 and perform machining with the operator manipulating the nozzle 150 to keep up with the condition of machining. However, this system is not in alignment with the degree of convenience offered by other features of the machining center. Therefore, there has been a standing need for a machining center equipped with such a feature as ensures that the machining fluid can always be directed to the aforementioned machining point.